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Flow disturbance due to microembolism in the cerebral microvasculature with an arcadal network was studied by a numerical simulation. A mathematical model for flow in the arcadal network was developed, based on in vivo data of cat cerebral microvasculature and flow velocity. The network model consisted of 45 vessel segments, and 25 branching points. To simulate microvascular responses to blood flow, the following three types of responses to wall shear stress were considered; non-reactive (solid-like), cerebral arteriole, and skeletal muscle arteriole-like responses. The numerical calculation was carried out in the condition where a feeding arteriole was occlused. Flow changes in efferent vessels were evaluated for assessment of blood supply to the local area of cerebral tissue. The present simulation has demonstrated that blood flow in efferent vessels was influenced by the topology of the vascular network and the response pattern in single vessels. The arcadal structure of arterioles might be most effective in response to flow disturbances in efferent vessels.

Autologus veins have been used clinically as a bypass conduit for reconstruction of small arteries, but there are few data available for microvascular response to arteriovenous (AV) shunting. This study was aimed to evaluate microvascular hemodynamic changes induced by creating AV anastomosis in rat hindlimb. Using intravital fluorescence videomicroscopy, we measured velocities of red blood cells (RBCs) flowing in the microvascular network in the control state, in the occlusion state where the superficial femoral artery (SFA) was occluded, and in the AV shunting state where the AV anastomosis was opened after occlusion of SFA. RBC velocities were measured in 155 capillaries of 6 rats using a dual window method and a frame-by-frame technique. The mean velocity and the coefficient of variation were 0.61 mm/sec and 0.90 in the control state, 0.34 mm/sec and 1.30 in the occlusion state, 0.83 mm/sec and 1.24 in the AV shunting state, respectively. These indicated that hemodynamic heterogeneity among capillaries increased with decrease in mean velocity following the arterial occlusion, while the AV shunting augmented the heterogeneity with increase in mean velocity. Capillaries with low perfusion (0.1 mm/sec) or high perfusion (1.0 mm/sec) were 5.8% or 20.6%, 29.6 or 5.2%, and 22.6 or 30.3% out of all measured capillaries in the control, occlusion and AV shunting conditions, respectively. In conclusion, AV shunting increased capillary perfusion and also its spatial heterogeneity, preferentially inducing high velocity in the microvasculature.

Vascular remodeling induced in rat limb by arteriovenous (AV) shunting was investigated by evaluating changes in vascular diameter and cell morphology. In Wistar rats, a vein graft was implanted in situ in the hind limb. Flow-rate in the grafted vein was assessed by measuring flow in the common femoral artery using an ultrasonic flowmeter. Nuclei and actin filaments of the venous wall were stained with propidium iodine and phalloidine-FITC, and the samples were observed using confocal laser microscopy. The grafted veins became circular in cross-section with increase in diameter during two weeks after AV shunting. Owing to the increase in diameter, the estimated wall shear stress was not increased so much as the flow-rate. The confocal laser microscopic observation showed that endothelial cells (ECs) and smooth muscle cells (SMCs) in the grafted veins were either aligned well (2 out of 8 samples), or ECs were denudated and SMCs were disrupted (in 6 out of 8 samples). The cell density of ECs was unchanged from the control level. In conclusion, the grafted vein was remodeled with morphological changes in ECs and SMCs during 2 weeks after AV shunting.

Capillary angiogenesis and remodeling induced by arteriovenous (AV) shunting in rat hind limb was investigated by evaluating changes in capillary density and diameter in the skeletal muscle subject to retrograde flow and high pressure. Wistar rats were used, and an AV anastomosis was created in the hind limb. Two weeks after AV shunting, the microvasculature in the limb was visualized by GS-lectine, and the samples were observed using confocal laser microscopy. The capillary density were increased by approximately 150% for small vessels (13 microm in diameter) under retrograde flow condition, but no change appeared for large vessels (13 microm in diameter). The capillary diameters were not significantly different between control and chronic condition. In conclusion, retrograde flow produced by AV shunting increased capillary density but it did not change the capillary diameter significantly.